Prosthetic implants can be used to replace natural joints that have been damaged or have deteriorated. For example, hip joint replacement surgery includes implanting a prosthetic femoral component into a prepared cavity in the femur of a patient. The femoral component is secured within the femur by an interference fit and bone ingrowth, by bone cement, or by a combination of these techniques.
Revision surgery, or replacement of a previously implanted prosthesis, may be required in some cases, usually due to long-term wear and/or subsidence of the implant.
In a revision procedure, the implanted prosthetic component is first removed from the medullary canal of the femur. Any bone cement used to secure the removed implant, and any cement-retaining plugs, must also be extracted, typically by drilling and reaming. After removal of the bone cement and plug, much of the cancellous bone is removed and usually only cortical bone remains. The resulting cavity will normally be larger than is desired to accommodate a new prosthesis, and the cortical bone will not allow cement inter-digitation to an extent sufficient to support the new prosthesis.
To reduce the size of this cavity or canal in the bone, morsellized cancellous bone from a donor can be placed in the femoral canal. This bone matter is compacted against the cortical bone with a tamp. FIG. 1 shows a typical prior art tamp 5 having a smooth outer surface that matches the contour of the prosthesis to be implanted. See also, U.S. Pat. No. 5,470,336, which is incorporated by reference herein. Alternating steps of adding bone matter and compacting the bone matter with tamps of decreasing size can be used to size the canal to generally conform to the shape of the implant.
During such a process, the cancellous bone should be sufficiently compacted to remain intact as the new implant and/or bone cement are inserted into the canal. Since the surface of the compacted bone matter interfaces with the bone cement, and/or the prosthetic implant, the compacted bone must be able to withstand shear forces that occur at the interface with the bone matter. If the cancellous bone is not adequately compacted, the strength of the interface surface can be compromised resulting in an unsuccessful revision.
While implant-shaped tamps can provide sufficient radial compaction of the morsellized bone, only limited axial compaction is achieved. The absence of adequate compaction in a longitudinal (axial) direction can leave the compacted bone matter vulnerable to damage from shear forces that result following implant revision surgery.